Enantiomers and barriers to racemization of sterically hindered N‐aryl‐ and N‐heteroarylpyrroles

The N‐aryl‐ and N‐heteroaryl‐2,5‐dimethylpyrrole‐3‐carbaldehydes 2–8 have been synthesized by condensation of hexane‐2,5‐dione with the appropriate amine and subsequent Vilsmeier‐Haack formylation of the pyrrole ring. Diastereomeric association complexes of the racemic pyrrole 8 were studied by pmr chemical shifts and the splittings induced by (+)‐1‐(9‐anthryl)‐2,2,2‐trifluoroethanol. Enrichment of the enantiomers M and P of 2 and 6 was achieved by liquid chromatography on triacethylcellulose. The barrier to partial rotation about the C‐N bond in 6 was determined by thermal racemization and its lower limits in 2 and 8 were estimated.